The shoulder joint is composed of a complex system of multiple muscles, tendons and ligaments. When functioning properly, these structures stabilize the head of the humerus within the Glenoid cavity. The four rotator cuff muscles surround the shoulder joint, blend with the capsule, and grasp their four points of attachment to the humerus, thus maintaining the integrity of the joint by acting as ligaments as well as moving the humerus.
Various exercise devices have been constructed to aid in the strengthening of the muscles that form the rotator cuff. The goal of such activity is to better stabilize the head of the humerus within the Glenoid cavity, especially during times of increased external loading as experienced during a throwing motion. Utilization of weighted dumbbells such as U.S. Pat. No. 460,270 issued to Somerby and U.S. Pat. No. 1,013,782 issued to Koch can be used to isolate and strengthen the muscles of the rotator cuff. However, strengthening achieved through dumbbell exercises does not fully prepare the shoulder joint for the type of loading seen during actual throwing activity. Dumbbell training does not simulate an actual throwing motion and therefore muscular development gained through such exercises may not be fully beneficial during actual throwing activities.
One general category of devices that have been proposed to strengthen the muscles of the rotator cuff is elastic band based designs. U.S. Pat. No. 4,268,031 issued to Schomburg describes a hoop with a hand-grip in its center with multiple elastic lines connecting the central handle to the parameter of the hoop. An oscillating motion is performed in an attempt to strengthen the muscles of the rotator cuff. This design only allows for a very short range of motion compared to the very long range of motion of an actual throwing movement. Utilizing similar elastic bands, U.S. Pat. No. 6,319,179 issued to Hinds describes a system of elastic cords that may be attached to a stable frame, such as a doorway. The cords pull against the general forward movement of the users hand during a typical throwing motion. Problems with this design include an unrealistic loading pattern for the throwing motion and the need of a stable frame for attachment.
Oscillating movements of a weight can be used to strengthen the muscles of the rotator cuff Spring or metal strips can be utilized to produce the desired oscillating effect. U.S. Pat. No. 5,147,262 issued to Hymanson describes a thin metal strip that is held at its midpoint. The user moves their hand back and forth along a short linear path. The device provides acceleration and deceleration forces at the endpoints of this short range of motion movement. A drawback with this design is its inability to strengthen the appropriate muscle groups through a complete range of motion similar to one that is experienced during a throwing motion. U.S. Pat. No. 5,474,511 issued to Dantolan describes a rod with a weight that slides along the rod. Springs decelerate the moving weight as it approaches the rod handles. The handles are positioned at the ends of the rod. A problem with this design is that it does not allow for a relaxed, free-fall segment of the simulated throwing motion. Another problem concerns the inability for an accurate throwing motion to be performed given the positioning of the devices handles at the ends of a long rod. U.S. Pat. No. 3,545,121 issued to Misko describes a device similar to that of U.S. Pat. No. 5,474,511 but to be utilized as a toy rather than as a training tool. U.S. Pat. No. 5,674,162 issued to Ellingson describes a shoulder rehabilitation device that is based a design of a hollow hoop with a central hand grip where said hollow hoop contains a moveable weight. As the user generates the required hand motion to keep the weight traveling around the hoop the user's shoulder muscles are exercised. Shortcomings of this design include that it only allows for training over a relatively short range of motion and that the movements trained do not accurately simulate an actual throwing motion.